1. Field of the Invention
The present invention generally relates to driving ropes. More particularly, the invention relates to a driving rope for use in shifting a printer carriage shifting, for example, a carriage for a printer or plotter in a word processor, or a mirror or a lens in a xerographer.
2. Description of the Prior Art
For shifting the printing head of a printer, plotter or the like, it is customary to employ a timing belt, i.e. an endless belt, such as a V belt formed with internal rack-teeth or a wire rope consisting of a plurality of bare metal wires twisted together.
In the system using a timing belt, which is illustrated in FIG. 5, a carriage 2 is attached to a timing belt 1 which is thrown over a pair of sprockets 3,3 installed with an appropriate spacing, with teeth 1a on the inner surface of said timing belt 1 being engaged with teeth 3a of said sprockets 3,3, so that the rotation of the sprockets 3 is transmitted to the timing belt 1. To shift the carriage 2 in this arrangement, the above-mentioned sprockets 3,3 are rotated to drive the timing belt 1. Here, the accuracy of carriage shift is assured by the positive engagement of teeth 1a of the timing belt 1 with teeth 3a of the sprockets 3,3.
However, since a timing belt 1 of this type cannot be easily twisted or otherwise deformed, the system is of necessity bulky and cannot be used for a compact printer built into a personal word processor or the like. It is also difficult to apply this system to a plotter or the like which demands a complicated motion of the carriage. Furthermore, since a timing belt 1 of this type is fixed in length and in the arrangement of inner teeth 1a, it can be applied to printers of a given specification only, thus lacking in universality.
On the other hand, when a wire rope is used as a drive means for shifting the carriage, the flexibility of the wire rope does not cause the above-mentioned problems with a timing belt, for as shown in FIG. 6, a wire rope 4 can be easily routed and thrown over pulleys 5,5 in a desired manner.
However, when the pulleys 5,5 are driven in such an arrangement, the wire rope 4 tends to slip so that the carriage cannot be accurately shifted.
To prevent the idle rotation of the pulleys 5,5, it has been proposed to secure both ends of a wire rope 4 to a drive bobbin 6 and wind the wire rope a few turns on the drive bobbin 6. In this system, as the drive bobbin 6 is driven, the wire rope 4 is paid out and taken up to shift the carriage 2.
However, it is troublesome to secure both ends of the wire rope 4 to the drive bobbin 6 and wind the wire rope a few turns on the bobbin. It is also a delicate work to adjust the tension of the wire rope.
Furthermore, even in the above arrangement, the tension of the wire rope 4 varies between the case in which the printing head 7 mounted on the carriage 2 is printing and the case in which it is not, and in winding the wire rope 4 on the drive bobbin 6, the winding position of the rope 4 tends to vary or one turn of the wire rope 4 tends to lie over another so that the accuracy of carriage shift is adversely affected to cause a variation in printing position.